The applicant institution is applying to join the ongoing Diabetes Control and Complications Trial (DCCT) as a participating center. The objective is to test the hypothesis that two treatment regimens resulting in statistically significant and clinically meaningful differences in blood glucose levels will result in clinically significant differences in the rate of appearance or progression of the early vascular complications of insulin dependent diabetes mellitus (IDDM). The two treatment regimens consists of (1) Intensive insulin therapy - 3 or more daily injections of insulin with the goal of normal blood glucose and glycosylated hemoglobin levels and (2) Conventional insulin therapy - not more than 2 daily injections of insulin with the goal of rendering the individual free of symptoms attributable to hyperglycemia and glycosuria. Retinopathy will be the principal outcome to be studied, with nephropathy, neuropathy and cardiovascular disease to be studied secondarily. Subjects will be randomized into the two treatment regimens and will be stratified as to duration of IDDM, allowing the evaluation of the treatment modalities as primary prevention and secondary intervention strategies.